This is a resubmission of the first competitive continuing application requesting NIH/NCRR support for the next 5 years of the UC Davis Mutant Mouse Regional Resource Center (UCD-MMRRC). The overall objective of the UCD-MMRRC is to serve as a component of the MMRRC National Program, to accept, maintain, and distribute mutant mouse strains for use in biomedical research. The MMRRC program accepts transgenics, knockouts, and all other kinds of mutant mouse lines at no cost to the donor, and after SPF-rederivation and cryopreservation, distributes breeding stock orgermplasm of genetically, and in many cases phenotypically verified mice for a small fee to requesting investigators for non-commercial, academic research purposes only. The UCD-MMRRC currently has a census of >9000 mutant strains maintained as either actively breeding mousecolonies, frozen embryos or germplasm, and/or embryonic stem cell clones. Further, the UCD-MMRRC serves in a coordinated network with 3 other regional MMRRCs as a center of excellence engaged in research and teaching on the biology of the laboratory mouse, providing the scientific community with professional expertise in mutant mouse biology, colony management, conventional and advanced genotyping and phenotyping capabilities, clinical and anatomic pathology services, strain rescue, infectious disease diagnostics and health care, and other areas. In keeping with this mission, this application states 4 interconnected Specific Aims that focus on continuing maintenance of mutant mouse lines in the resource, acceptance of new lines into the resource, research and development projects that eventually will be transferred to the resource to improve its functional efficiency and capabilities, and finally to provide opportunities for outreach and education and training in mouse biology. These Specific Aims are facilitated by closely linked faculty expertise of the UCD Center for Comparative Medicine (CCM), the UCD Mouse Biology Program (UCD-MBP), and the Schools of Medicine and Veterinary Medicine. These relationships allow leveraging of MMRRCsupport, resulting in expanded opportunities for, and benefit to, the MMRRC National Program and the biomedical and behavioral scientific research community.